The man, Luis Picaso, 59, suffered second and third degree burns over 60 percent of his body, including his upper torso and arms, in the fire late Saturday night, said the investigator, Bill Tweedy at the Vallejo Fire Department in an interview Tuesday. The victim was listed in critical condition this morning at the University of California at Davis Medical Center, a spokeswoman said.

Picaso lives in a downtown apartment in a four-story building that once served as a hotel, Tweedy said. The fire in the second-floor apartment caused US$30,000 in damages, but the fire was mostly contained because a sprinkler system was activated. The man was found in a bathroom by firefighters.

Tweedy said a thorough investigation showed nothing else in the bathroom could have ignited the fire, such as matches or a lighter. "The only thing that was a power source was the cell phone," Tweedy said.

Tweedy said it was a "pretty new cell phone" that was just a voice device, and not a smart phone. He refused to disclose the brand, saying it was not the kind of accident that would necessitate a manufacturer's recall.

"I think it was just a malfunction," Tweedy explained. "The phone was in his pants pocket and he was leaning against a chair asleep, so one button was depressed. That meant power was going through the phone, and the phone overheated."